Most volcanoes form a cone, as you can see in the graphics above. During an eruption the volcano flings out material which builds up, layer upon layer, and often forms this form of landscape. There are different types of cones: stratocones, spatter cones, ash cones, tuff cones, and cinder cones.

What a volcano needs as a kind of “driving force” is a magma chamber deep below the ground. The depth and size of such chambers varies for each volcano. Some have more than one chamber in different depts.

If new magma arrives in a magma chamber, the pressure rises. The magma starts to rise through cracks. When this stress is high enough, it starts cracking rocks. This causes volcanic earthquakes. Those earthquakes are rather weak most and often hardly felt by the people living above such a magma chamber. The strongest volcanic quakes are around magnitude 4. Such volcanic quakes come in swarms. There were thousands of quakes during the month before the submarine eruption in El Hierro.
The magma may eventually start a dyke intrusion. Very very often there is not enough magma or no new magma is arriving and an earthquake swarm dies down and just stops without an eruption happening.

This image shows the red glowing lava in motion on Hawaii while the next image shows an ancient version on Teneriffa.

Rope Lava, Image by author

Caldera

Caldera formation shown at the example of Crater Lake, Oregon.

We like to disuss calderas on VC. 😉 A caldera is the result of the collapse of a magma chamber of the volcano. Calderas are much bigger than craters: Sometimes new volcanoes grow out of a caldera. The formation of a caldera can have disastrous effects especially when a submarine caldera is formed and water streams into the hot, new caldera, like it has happened at Krakatau 1883.

Crater Lake oregon. Image Wikimedia Commons

Other features which you hopefully never get to see live but they are discussed here and one might stumble over the results climbing a volcano.

Pyroclastic flow.

A Pyroclastic flow happens when the ash column breaks down under its own weight. But they can also happen when a dome collapses as we saw recently at Sinabung (video above) or like at Mount Saint Helens when a directional blast happened. The resulting ignimbrites can be found on many volcanoes.

The greenish layer is made of ignimbrites. Image Wikimedia Commons.

Lahar
A Lahar is a mixture of volcanic materials with water and is a Javanese (Indonesia) word that describes mudflows. Lahars are called Jökullhlaups in Iceland.

A lahar may happen during a volcanic eruption when some kind of interaction between the volcano and
water. Either a glacier is being melted or a lake is involved or it is raining heavily. Many eruptives from a volcano contain a lot of water/steam so rain often comes automatically with volcanic ash clouds.

Mount Saint Helens 1982- Image Wikimedia Commons.

Lahars have the consistency of liquid concrete and may endanger people far away from the erupting vent.

While trying to write this post I discovered how difficult it is to describe volcanic terms with very little words just to explain the terms we on VC use so frequently. All newcomers to this blog please note that this only the very basic about volcanoes written by a non-expert volcanophile. Again… Every volcano is different. No 2 craters look exactly alike, neither do all the other volcanic features. I would like to continue with the different kinds of eruptions next time.
Part 1 of this series: